This invention relates generally to fans for moving air. More particularly, the invention relates to an improved axial flow fan. The fan may either be shrouded or unshrouded. The embodiment of the invention that includes a shrouded fan also includes a fixed orifice to be used in conjunction with the fan.
Axial flow fans are used to cause air movement in a wide variety of applications, including building heating, ventilating and cooling systems and engine cooling systems, to name just a few.
In most applications, the air stream entering a fan is nonuniform and turbulent. These conditions result in unsteady air flow at the leading edge of the fan blade and pressure fluctuations on the surface of the blade. These pressure fluctuations are responsible for noise that is radiated from the fan. The sound level of the noise produced by the blade is a function of the relative velocity between the air and the fan blade. The relative velocity, in turn, increases with linear blade speed, which is a function of fan rotational speed and distance on the blade from the fan center of rotation. Radiated noise from the fan also increases with local blade loading, which is a function of the amount of work being done at a particular location on the blade, the pitch and camber of the blades and blade solidity (that is, the total area of the swept disk of the fan covered by blade).
In general, a quiet fan is also an efficient fan, having a lower input power requirement for moving a given amount of air as compared to noisier fans.
Advances in materials technology and fabrication techniques have led to the use of plastics in a wide variety of new applications. Modern plastics can be strong, durable, damage resistant, lightweight and competitive in manufacturing cost with other materials. Moreover, the ability to easily mold plastic material has enabled the mass production of components in complex shapes that have previously been difficult and uneconomical to manufacture.